Like fuck, every fucking problem is an exception to the rule. It's just really hard to conceptualize, and I still have no idea how molarity or fucking moles work or anything.
If you're having trouble you might consider looking at
Khan Academy or
Crash Course among other things on YouTube. I suggest that before you start on problems you have a firm grasp of the theory, i.e. you can explain a theory or concept without having to refer to a book. You can't progress to more complicated theories if you don't understand the basics, in this case units.
As for your specific problem, to understand molarity obviously you have to know what mole is first. Firstly we use moles because it would be incredibly difficult to perform equations using the number of individual atoms, molecules, ions, etc. Instead we simplify it into something called moles.
1 mole is = 6.022 x 10^23 (a.k.a Avogadro's number) atoms, molecules, ions, etc. Say we have 1 mole of Carbon (C). That means that we have 6.022 x 10^23 atoms of carbon. Likewise, if we have 1 mole of Oxygen (O2), we would have 6.022 x 10^23 molecules of O2.
Now 6.022 x 10^23 is an extremely hard number to visualise. So if you want to see it in terms of weight you would use the formula m = n * M (m= mass (grams), n= moles, M= molar mass (grams/mole)). From the periodic table Carbon has a M of 12.01 g/mol. Therefore 1 mole of Carbon would weigh about 12.01 g.
m = 1mol * 12.01g/mol = 12.01g
But of course it differs for different elements and molecules. Lets use 1 mole of O2.
m = 1mol * (16.00g/mol *2) = 32.00g
So while O2 and Carbon are equivalent in their number of molecules and atoms respectively (6.02 * 10^23 atoms of molecules), O2 is more then twice as heavy then C.
Molarity is defined by the equation c = n/V (n= mole, V = volume (L)). Now we looked at before the idea of moles as the amount of molecules, atoms, ions, etc. So lets first picture volume as a box with dimensions 10 cm for all length, width and height. This would give the box a volume of 1 litre. Now picture yourself placing 1 mole of O2 in the box. This would give you a molarity of 1.
c = 1mole/1litre = 1 M.
Molarity is simply the amount of molecules, atoms or ions that occupy a space (or in a solution)
